The present invention relates to a metal pouring apparatus and method.
When a bottom pour vessel such as a ladle is prepared for teeming, it is common to inject gas into its molten contents in the vicinity of the vessel well area which leads to the bottom pour opening of the vessel. Gassing is performed for several purposes including rinsing; clearing the relatively-cool well area of solidification products; lowering and/or equalising the temperature throughout the melt and redistributing chilled melt adjacent the sides and bottom of the vessel; and stirring to distribute alloying additions uniformly in the melt. Gas injection is also frequently used for introducing particulate matter to the melt for dissolution, the gas being a carrier therefor.
Gassing has hitherto been accomplished in several ways, each having disadvantages. Lancing involves lowering a refractory-coated pipe or lance into the melt. The lance is a costly item and has but limited life, for it is subject to deleterious attack or burn-through in the region of the slag layer floating on the melt. In another approach, the vessel lining is provided with an opening in which a porous plug is seated. The plug has a gas-supply pipe depending therefrom which passes through an aperture in the exterior of the vessel. The gas supply is then connected beneath the vessel to the pipe. Leakage of melt between plug and lining can occur especially if either is damaged or eroded, and hence use of such a plug for gassing has potentially grave hazards.
Where teeming from bottom pour vessels is controlled by sliding gate valves, it is inconvenient to employ a well plug as just outlined. Gassing may then be accomplished through the valve which has a special valve closure element furnished with a porous plug, the plug being gas permeable but impenetrable by the melt. See U.S. patent specification No. 3,581,948 assigned to Interstop A.G. It is not always convenient nor cost effective to use such special closure elements. Alternatively, the well or part thereof may be formed by a gas-porous brick, through which gas is pumped to the teeming passage. See. G.B. patent specification 1,351,618 to Didier Werke A.G.
Steelmakers often wish to fill the bottom pour opening with a silicious filler (sand or a mixture of sand and graphite) before the melt is introduced to the vessel. This is inter alia to prevent freezing in the opening and ensure teeming commences cleanly when the sliding gate valve is opened for the first time. With gassing arrangements as disclosed in the aforementioned patents a significant risk may arise that the gas will upset the silicious filling. One of our aims has been to devise means for gassing which is capable of avoiding this risk.
In practice, of course, teeming from a vessel is not always a one-shot operation. Commonly teeming is interrupted, as where several moulds are to be filled. The silicious filling is lost upon start of the first teem, but gassing may still be desired during later teems. The arrangement we have devised can be used in this way and no special valve closure elements are required.